# 构造函数
def fib(input_number):
    num = int(input_number)
    if num == 1 or num == 2:
        return 1
    else:
        return fib(input_number - 1)+fib(input_number - 2)
    
input_number = int(input("请输入第n项:"))    
result = fib(input_number)
print(result)


# # 非递归
#
# n = 6
# fibs = [1,1]
#
# for i in range(2,n+1):
#     fibs.append(fibs[i-1]+fibs[i-1])
#
# print(fibs[n-1])